1. Field of the Invention
This invention concerns fluid pressure actuator mechanisms and more particularly such mechanisms which have a position sensing capability associated with the output member.
2. Description of the Prior Art
It is often desirable or necessary in applications of fluid pressure actuators such as hydraulic cylinders to have some means for generating a signal indicative of the relative position of the output member associated therewith for purposes of control of systems into which the actuators are integrated. This is particularly so in automated manufacturing systems such as are utilized in automotive manufacturing operations. The traditional approach at providing this capability has been the utilization of switches mechanically actuated by the output member, usually with the use of associated cam or lever arm assemblies mechanically activated by stroking of the output rod. However, in many applications such as the highly automated automotive manufacturing operations referred to, extreme requirements of reliability and long life are necessary, since such equipment is normally operated for many thousands of hours and with minimal maintenance. The situation is further intensified by the great penalty involved in any down time of the equipment which could result from simple failure of the device or from the resulting damage to the remaining portions of the equipment due to failure of the actuator to operate properly.
In this context, mechanical actuation of limit switches which have been mounted in relatively exposed conditions have created great problems since the environment in such applications often times include oil and coolant splash or impacting of the mechanism by virtue of its exposed position. The presence of moving parts also introduces the element of mechanical wear and other factors all of which have produced a less than satisfactory performance of such arrangements.
A previous attempt to provide such position indication by sensing the position of an internal portion of the movable actuator member has similary included a switch which is operated by a movable member engaged with some portion of the movable output member within the interior of the actuator device. Since mechanical movement is still involved, the aforementioned problems are not solved by this approach and additional problems of proper sealing of the element extending into the interior of the device are created. These factors have created a generally unacceptable performance history of such devices.
Another problem encountered in such devices is false triggering of the switch caused by a momentary closing or opening of the switching device resulting from shock or vibrational impacts of the switch.
It is therefore an object of the present invention to provide a position sensing arrangement for fluid actuator devices which does not involve the use of a mechanical actuation of a switching device and is mounted in an internal installation sensing the position of a movable member within the confines of the actuator device housing.
It is another object of the present invention to provide an arrangement for obviated false triggering caused by momentary closings or openings of the switch assembly.